1. Field of the Invention
The present invention relates to a doctor for creping tissue from a surface of a Yankee dryer. More particularly, the present invention relates to a doctor having a blade, the angle of which may be selectively changed.
2. Information Disclosure Statement
In the manufacture of tissue, a web of tissue is formed on a forming wire and is subsequently guided around a Yankee dryer. A Yankee dryer is a cylindrical dryer having a diameter of approximately 20-30 foot and is internally heated by steam. The Yankee dryer defines a smooth outer peripheral surface on which the tissue is guided and dried.
A plurality of doctor blades are disposed in abutting relationship with the heated surface of the Yankee dryer at a downstream location thereof for doctoring the tissue from the heated surface of the dryer when the tissue has been sufficiently dried by the Yankee dryer.
The aforementioned plurality of doctors includes a skinning doctor disposed upstream and a cleaning doctor disposed downstream, with a creping doctor disposed between the skinning and cleaning doctors.
During the production of tissue, the creping doctor is disposed in operative cooperation with the surface of the dryer, while the skinning doctor is disposed in a position away from the dryer surface.
With particular reference to the creping doctor, the doctor blade is disposed at an angle relative to the heated surface of the dryer for creping the tissue off of the heated surface. Such removal of the tissue from the heated surface generates minute ripples in the removed tissue for providing the required bulk, softness, and other desirable qualities of the resultant tissue.
More specifically, the aforementioned angle of the blade relative to the dryer surface has a profound effect on the quality of the resultant tissue.
However, during use of the creping doctor due to the frictional engagement of the operative edge of the blade against the surface of the dryer, there exists a tendency for the blade to wear, thereby altering the aforementioned angle.
Consequently, in order to maintain an optimum quality of the resultant tissue, it is necessary to adjust the position of the doctor so that the aforementioned angle is maintained.
Additionally, it is important that the angle of the blade relative to the dryer surface be adjustable in order to accommodate various types of tissue to obtain the aforementioned optimum qualities thereof.
The present invention provides a unique means for adjusting the aforementioned angle. Basically, the present invention permits the doctor and the blade secured thereto to be selectively pivoted about an axis which extends along the operative edge of the blade.
Furthermore, the present invention includes loading means which permit the blade to be moved away from the heated surface of the dryer and back again to the operative disposition thereof so that the angle between the blade and the dryer surface is restored.
In the prior art arrangements, because the doctor is movable about a pivotal axis which does not coincide with the operative edge, difficulties have been experienced in maintaining the required angle of the blade relative to the dryer surface.
Therefore, it is a primary objective of the present invention to provide a doctor for creping tissue that overcomes the aforementioned disadvantages of the prior art arrangements and which provides a significant contribution to the art of creping tissue from a surface of a Yankee dryer.
Other objects and advantages of the present invention will be readily apparent to those skilled in the art by a consideration of the detailed description contained hereinafter, taken in conjunction with the annexed drawings.